In many fields, for example in third and higher generation base stations of mobile communication networks or mobile communication devices, bandwidth-optimized modulation schemes are used for transmitting information. Bandwidth-optimized modulation schemes typically require a non-constant envelope, and thus have a relatively high peak-to-average power ratio (PAR). Linear amplifiers such as class AB amplifiers offer high linearity but must be driven with a high back-off from the maximum (saturated) output power to achieve good linearity across a wide operating range. Typically, RF power amplifiers, of whatever class, e.g., type AB, or so-called switched mode (also: switch mode) amplifiers of type D, E, F, etc. only achieve high efficiency when operated close to their maximum saturated power level. Thus, backing-off a class AB amplifier typically results in lower transmitted power, and thus reduced overall power efficiency.
Instead of using a single amplifier, several individually activatable amplifiers may be used so that for small amplitudes/powers only one or a few amplifiers are active, whereas for large amplitudes/powers more and eventually all amplifiers are used. The outputs of the individual amplifiers are combined by means of a power combining network. The power combining network typically needs be designed carefully to maintain the signal integrity and to achieve a high combining efficiency. Typical combining networks are based on distributed transmission line elements and suffer therefore from bandwidth limitation and cannot be integrated easily on chip level.